Wu

Chinese 無, "not, nothing, lacking, without."

A key word and philosophical basis of Buddhism, especially Ch'an and Zen.

Wu is also used as a basis for meditation (as a Hua tou or mantra).

'Enlightenment', or Wu, is the heart of Zen; but what is this Wu experience, and is it one, or many? Wu is the direct experience of beholding, unfolding, or realize the Mind-essence in its fullness...

Wu means ‘to awaken to the fact', or, loosely, 'to understand'...

...the Buddhas and Patriarchs who incarnated in this world, through the use of thousands of words and various methods, preached either the Doctrine, or Zen. All their teachings were but instruments to crush the habitual ‘clingings’ infecting human thought. There is no Dharma in the sense of something real or concrete that which they have handed down to us. The so-called practice or work is merely a method for purifying the shadows of cur habitual thinking and flowing thoughts. To concentrate all one's efforts to this end is called ‘work'. If suddenly the surging thoughts stop, one sees clearly that one's self-mind is originally pure, genuine, vast, illuminating, perfect, and devoid of objects. This is called Wu [Japanese: satori]. There is nothing outside of the mind, nothing which can be worked upon, and nothing to be enlightened. . . • However, the egotistic passions [ie. lust], long-accumulated and rooted within us, are difficult to wipe out." - C.C.Chang, The Practice of Zen (1960)